Your not trying to do a 10mm hole in one go are you?Done one and a half hole on the 20mm thick steel plate now by used one battery. Need to recharge it, which mean need 4 charges to make the job done. Should be able to try it on boat tomorrow.
Clearance hole for M10 needs to be minimum 11mm. 12 should be fine.10mm drill holes are too tight for M10 bolts when the steel plate is attached to the coupling. Maybe because the holes have a bit angle while drilling. Need to buy a 12mm drill bit to make it bigger and try again.
Good question, from the original photo it looks like the keyway protrudes quite a long way into the shaft so just check the spacer isn't fouling this.Remarkable! Does your spacer cover the end of the key? If the keyway is closed then that would prevent movement.